Fixed value residual stress test block and manufacturing and preservation method thereof

ABSTRACT

A fixed value residual stress test block, comprising a main body ( 1 ) and two welded blocks ( 2 ); the main body ( 1 ) and the welded blocks ( 2 ) are all rectangular metal blocks; the welded blocks ( 2 ) are welded onto the two opposite side surfaces of the main body ( 1 ); the main body ( 1 ) is deformed under the upper and lower pressures and generates residual stress. The fixed value residual stress test block has a simple structure.

This application is a divisional of U.S. patent application Ser. No.14/647,813, filed Sep. 28, 2015, which is a National Stage ofinternational patent application PCT/CN2013/072495, filed Mar. 12, 2013,which claims foreign priority to Chinese patent application201210498787.X, filed Nov. 29, 2012 and to Chinese patent application201210500267.8. These patent applications and all other extrinsicreferences contained herein are incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a fixed value residual stress testblock and manufacturing and preservation method thereof. The fixed valueresidual stress test block is adapted to correct an ultrasonicnon-destructive testing system for residual stress.

DESCRIPTION OF THE RELATED ART

The non-destructive testing for residual stress is receiving much moreattention, and the non-destructive testing method having vast potentialof development at present is the residual stress testing with ultrasonicmethod. The ultrasonic method mainly tests residual stress by means ofultrasonic critical refraction longitudinal wave. The theory ofultrasonic stress testing has been very mature. However, the testingobject of this method is relative value of residual stress, according tothe theory. In order to test the absolute value of residual stress, itis necessary to develop a quantized standard test block for residualstress to correct a testing result and a testing system.

The current study relating to a standard test block for fixed residualstress aims mainly at a x-ray diffraction. In this case, the metalpowder of material to be tested is cast as a test block of a certainsize, and the residual stress is standardized on the basis of thelattice change of the cast test block. Moreover, the researchers of theUK bend steel material to bow shape, so that a residual stress testblock is manufactured by bending. The structure of these test blocks isvery special, resulting in that the manufacturing method is toocomplicated to be achieved. For this, it is hoped to get a fixed valueresidual stress standard test block of simple structure, which isaccurate and reliable and obtained by a simple method.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a fixed value residual stresstest block and manufacturing and preservation method for correcting anultrasonic non-destructive test system for residual stress, so as todetect the absolute value of residual stress accurately and reliably.

The fixed value residual stress test block comprises a main body and twowelded blocks. Both of the main body and the welded blocks arerectangular metal blocks. The welded blocks are welded to two oppositesides of the main body. The main body deforms due to bearing a pressurein up and down direction, and generates residual stress.

The fixed value residual stress test block according to the inventionhas a simple, accurate and reliable structure.

The invention further provides a manufacturing method for fixed valueresidual stress test block, which has the following manufacturingprocedure: manufacturing main body of the test block and two weldedblocks; applying a pressure to the main body of the test block in up anddown direction so as to deform the main body to generate residualstress; welding the two welded blocks to two opposite sides of the mainbody; canceling the pressure applied in up and down direction.

The aforementioned method is very simple. The fixed value residualstress test block manufactured by the method is accurate and reliable.

The invention further provides a preservation method for fixed valueresidual stress test block. The test block is stored in an environmentwith constant-temperature of which the range is 2˜8° C., and is keptaway from impact and vibration.

The preservation method can make the residual stress test block maintainstable residual stress.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the side view of the fixed value residual stress testblock;

FIG. 2 shows the front oblique view of the fixed value residual stresstest block;

FIG. 3 shows the exploded view of position relationship between eachparts of the fixed value residual stress test block;

FIG. 4 shows the front oblique view of locating position of each partsof the fixed value residual stress test block;

FIG. 5 shows the welding process of the fixed value residual stress testblock.

SYMBOLS

1. main body, 2. welded block, 3. weld seam, 4. upper pressure-head ofcompression-testing machine, 5. lower pressure-head ofcompression-testing machine, 6. measurement area.

DETAILED DESCRIPTION

According to the invention, the fixed value residual stress test blockis manufactured by weld. According to the invention, two welded blocksare generally welded on symmetric positions of a pressed main body. Thetensile stress is generated to the welded blocks by rebound effect ofthe main body. The different deformation corresponds to the differentstress. The test block having desirable stress can be obtained bycontrolling the deformation of the test block via calculation based onthe theory.

The embodiment of the invention will be described in detail withreference to the drawings.

Take steel 45 for example, as FIG. 1 shows, the size of the main body 1is 30 mm×30 mm×130 mm. The size of the welded blocks 2 is 30 mm×5 mm×70mm.

Two welded blocks 2 are welded to both sides of the main body 1 of thefixed value residual stress test body. The welded blocks 2 are arrangedat central position of the main body 1. In a case that the main body 1is pressed by a compression-testing machine, the welded blocks 2 arewelded to the main body 1. The rebound effect of the main body 1generates a certain residual stress between the welded blocks 2 and themain body 1. The residual stress value of the test block can be known onthe basis of the deformation of the main body 1 and the welded blocks 2.The different deformation corresponds to the different stress.

The unidirectional pressure stress is generated by pressing the mainbody 1 of the test block within limit of elasticity. The main body 1will rebound after pressure being canceled. The welded blocks 2 and themain body 1 before rebounding are welded together by welding technique,so as to restrict and interact with each other. Then, the tensile stressor pressure stress is generated between the welded blocks 2 and the mainbody 1. According to this theory, the fixed value residual stress testblock can be manufactured by pressing and welding and controlling thedeformation of the main body 1 and the welded blocks 2. The weld seam 3is entirely continuous.

In the process of manufacturing the test block, the key point is theaccurate control for the deformation of the main body 1 and the weldedblocks 2. The accurate control for residual stress of the test block isbased on the accurate control for the deformation. However, thepreservation technique is also very important during the test blockbeing used.

The manufacture of the fixed value residual stress test block is asfollows:

Take steel 45 as manufacture material of the test block for example, asFIG. 1 shown, it is formed to be two parts of the test block. The sizeof the main body 1 is 30 mm×30 mm×130 mm. The size of the welded blocks2 is 30 mm×5 mm×70 mm. The surface roughness of the main body 1 and thewelded blocks 2 is less than or equal to Ra6.4.

The main body 1 and the welded blocks are tempered, so as to eliminateprocess stress of the test block and make the test block be in astress-free state.

According to the Hooke's law, the applied pressure, i.e. load applied bythe compression-testing machine to end surface of the main body 1 iscalculated, on the basis of the cross-sectional area of the main body 1and the welded blocks 2 and required stress value of the test block.

As FIG. 2 and FIG. 4 show, the two welded blocks 2 and the main body 1are closely attached together by bounding.

As FIG. 5 shows, the main body 1 is put between the upper pressure-head4 and lower pressure-head 5 of the compression-testing machine. Thecompression-testing machine is set based on predetermined (calculated)load to press the main body 1. The hollow arrows in the figure show thepressed directions. The 30 mm×30 mm surfaces of the main body 1 arepressed surface. After a calculation load being achieved, the load ismaintained stable for a while, and then the welded blocks 2 are weldedto the main body 1 in a case that the load is not unloaded. It isensured as far as possible that the main body 1 and the welded blocks 2do not have obvious deformation during welding. The contacted edges ofthe contacted surface between the main body 1 and the welded blocks 2should be entirely covered by weld seam.

After the welding for welded blocks 2 being completed, an air cooling isapplied to the test block in a case that the load is not unloaded. Afterthe test block being cooled, the compression-testing machine is removed,and the manufacture for the test block is completed. After then, thestress of the fixed value test block is measured and recorded, and iscompared to a theoretical value.

If the welded test block having different residual stress is required,it only needs to apply different pressure to the main body 1, and thenperform an operation according to aforementioned steps.

During correction of an ultrasonic non-destructive test system forresidual stress using the fixed value residual stress test block, adetection sensor is paced on the welded blocks 2 along the presseddirection of the main body 1, so as to couple the detection sensor tothe test block well. After being stable, it starts to detect and correctthe test block. As FIGS. 3 and 5 show, the fixed value measurement areas6 of the fixed value residual stress test block are on the outer sidesurfaces of the two welded blocks 2, and these two measurement areas 6are only suitable to a detection method of ultrasonic criticalrefraction longitudinal wave and a detection method of surface wave.

Currently, there are methods for eliminating residual stress in domesticand overseas, such as tempering, vibratory stress relief, ultrasonicwave impact, and natural stress relief. These methods achieves thatlocal organization of the welded piece is reorganized under the actionof alternative change of temperature and alternative load, such asvibration and impact, so that the residual stress is released. Thestable constant temperature may reduce the thermal expansion andreorganization of the test block, so that the residual stress may bemaintained for a long time.

For this, in order to make the fixed value residual stress test blockmaintain a stable residual stress, the test block should be stored inconstant temperature environment, such as calorstat, where thetemperature is 2° C.˜8° C., after the fixed value residual stress testblock being manufactured and the residual stress being measured, so asto eliminate the thermal expansion of the test block caused byalternative change of temperature, and to avoid the residual stress iscontinuously loosed. Furthermore, the impact and vibration which maycause the residual stress release should be avoided, during storing thetest block. The change of the residual stress of test block is regularlymonitored and recorded during storing the test block. The test blockshould be put back into the calorstat in time after correcting theultrasonic detection system for residual stress at each time.

What is claimed is:
 1. A preservation method for a fixed-value residualstress test block, comprising: storing said test block in an environmentwith constant-temperature of which the range is 2˜8° C.; and keeping thefixed-value residual stress test block away from impact and vibration;wherein the fixed value residual stress test block comprising a mainbody and two welded blocks, both of said main body and said weldedblocks are rectangular metal blocks, said welded blocks are welded ontotwo opposite side surfaces of said main body while said main body isdeformed under pressures in up and down directions such that, when thepressures on the main bodies in the up and down directions is removed,the rebound effect of the main body generates a residual stress betweenthe main body and welded blocks.
 2. The preservation method of claim 1,further comprising: monitoring the residual stress of the fixed-valueresidual stress test block for changes; and recording a detected changeof the residual stress of the fixed-value residual stress test block.